Software Interrupt Request Acknowledgment - NEC 78K0 User Manual

Figure 19-8. Interrupt Request Acknowledgment Timing (Minimum Time)
CPU processing
××IF
(××PR = 1)
××IF
(××PR = 0)
Remark 1 clock: 1/f
CPU
Figure 19-9. Interrupt Request Acknowledgment Timing (Maximum Time)
CPU processing
××IF
(××PR = 1)
××IF
(××PR = 0)
Remark 1 clock: 1/f
CPU

19.4.2 Software interrupt request acknowledgment

A software interrupt request is acknowledged by BRK instruction execution.
disabled.
If a software interrupt request is acknowledged, the contents are saved into the stacks in the order of the program
status word (PSW), then program counter (PC), the IE flag is reset (0), and the contents of the vector table (003EH,
003FH) are loaded into the PC and branched.
Restoring from a software interrupt is possible by using the RETB instruction.
Caution Do not use the RETI instruction for restoring from the software interrupt.
CHAPTER 19 INTERRUPT FUNCTIONS
Instruction
(f : CPU clock)
CPU
Instruction
(f : CPU clock)
CPU
User's Manual U15947EJ2V0UD
Instruction
8 clocks
25 clocks
Divide instruction
33 clocks
*
32 clocks
6 clocks
PSW and PC saved,
Interrupt servicing
jump to interrupt
program
servicing
7 clocks
6 clocks
PSW and PC saved,
Interrupt servicing
jump to interrupt
program
servicing
Software interrupts cannot be
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